Proportional pressure control valve

ABSTRACT

The technical field of the invention generally concerns electronically controlled hydraulic valves adapted for use in electro-hydraulically controlled automotive transmissions. The proportional pressure control valve  20  includes a hollow cage  42  pierced by cage tank ports  52 , cage clutch ports  54 , and by cage pump ports  56 . The cage pump ports  56  receive fluid from a pump. The cage clutch ports  54  supply fluid to a hydraulic actuator, such as that for an automotive clutch. The cage clutch ports  54 . supply the fluid at a pressure that is proportional to an electrical control signal applied to a solenoid coil  252  of the valve  20 . The cage tank ports  52  return fluid from the valve  20  to a tank from which the fluid circulates back to the pump. Located in the cage  42  is a main spool  112  that is movable laterally relative to the cage  42  for controlling a flow of hydraulic fluid between the cage clutch ports  54  and either the cage pump ports  56  or the cage tank ports  52 . An electromagnetically operated pilot valve regulates a control pressure of fluid applied to a control pressure surface  138  at one end of the main spool  112 . A feedback pressure passage  126 , having a feedback restriction orifice  128 , couples the pressure of fluid in the cage clutch ports  54  to a feedback pressure surface  114  at the opposite end of the spool. The feedback restriction orifice  128  restrains the rate at which fluid may flow between the cage clutch ports  54  and the feedback pressure surface  114 . One embodiment of the valve  20  includes a pressure spike suppression check valve  504  for relieving any abnormally high pressure that occurs in the cage clutch ports  54 .

This application is a continuation of prior application Ser. No.08/960,971filed Oct. 30, 1997, now abandoned, which, in turn, is acontinuation of prior application Ser. No. 08/598,285, filed Feb. 8,1996, which issued as U.S. Pat. No. 5,836,335 on Nov. 17, 1998, which inturn, was a continuation of prior application Ser. No. 08/426,647 filedApr.21, 1995, now abandoned, which, in turn, was a continuation of priorapplication Ser. No. 08/034,188 Mar. 22, 1993, now abandoned, which inturn was a continuation of prior application Ser. No. 07/747,131 filedAug. 19, 1991, now abandoned.

TECHNICAL FIELD

The present invention relates generally to the technical field ofhydraulic control devices and, more particulary, to electricallycontrolled hydraulic valves.

BACKGROUND OF THE INVENTION

Automobiles, trucks, tractors, earth-moving vehicles, vehicles, and manyother different types of vehicles (hereinafter collectively referred toas automotive vehicles) frequently include an internal combustion enginefor powering their movement across the earth's surface. An automotivevehicle also includes a drive train for transmitting energy produced bythe internal combustion engine into movement of the wheels, drive tracksor similar means by which the vehicle is driven across the earth'ssurface. To effectively accommodate the power characteristics of theinternal combustion engine to the load of the vehicle that it must driveat various speeds over varying terrain, an automotive vehicle's drivetrain usually includes one or more transmission. Each transmission in anautomotive vehicle includes a transmission power input shaft thatreceives energy from the internal combustion engine's power outputshaft, and a transmission power output shaft for transmitting theengines energy onto the means for driving the vehicle across the earth'ssurface. Each transmission in an automotive vehicle also includes setsof gears, each one of which, when selected for coupling thetransmission's power input shaft to its power output shaft, provides adifferent speed ratio between the rotation rates, respectively, of thetransmission's power input and power output shafts.

To facilitate selecting a particular gear ratio and for smoothlyaccelerating an automotive vehicle from a stationary start, its drivetrain usually includes a clutch located between the automotive vehiclesinternal combustion engine and its transmission(s). This clutchselectively couples the internal combustion engine's power output shaftto the transmission's power input shaft. In one position of the clutch,it completely decouples the engine's power output shaft from thetransmission's power input shaft. In another position, the clutch of anautomotive vehicle provides a tight coupling between the internalcombustion engine's power output shaft and the transmission's powerinput shaft. In this tightly coupled state, the internal combustionengine's power output shaft and the transmission's power input shaftrotate at the same speed. However, most clutches for automotive vehiclesoperating in this tightly coupled state are capable of passing only somemaximum amount of torque from the internal combustion engine to thetransmission without slippage occurring in the clutch. If a torquegreater than this maximum amount is supplied to the clutch in itstightly coupled state, slippage occurs within the clutch that allows thepower output shaft of the internal combustion engine to rotate at aspeed different from that of the transmission's power input shaft.

Between these two extremes of clutch operation, either of beingdecoupled or of being tightly coupled, the design of most clutches usedin automotive vehicles permit progressively varying the tightness ofcoupling between the engine's power output shaft and the transmission'spower input shaft. In intermediate states between these two extremes,the clutch will transmit an amount of torque to the transmission withoutslippage that is less than the maximum amount that it will transmit whentightly coupled. Controllably coupling differing amounts of torque fromthe internal combustion engine to the means for driving the vehicleacross the earth's surface permits smoothly accelerating an automotivevehicle into motion. Controllably coupling different amounts of torquefrom the internal combustion engine to the means for driving the vehiclethrough the clutch is also useful, particularly for heavy industrialvehicles such as trucks, tractors and the like when shifting thetransmission smoothly from a set of gears having one ratio to anotherset having a different ratio.

Historically, a driver of an automotive vehicle usually operated itsclutch through a direct mechanical linkage between the clutch and aclutch pedal located in the vehicle's passenger compartment near thedriver. In some instances, a closed hydraulic system for operating theclutch by pressure on the clutch pedal replaces the direct mechanicallinkage. More recently, to provide automatic electronic control of gearratio selection, particularly in automotive vehicle's that include amicroprocessor, it has become desireable to control clutch operation bymeans of an electrical signal rather than by the driver pressing on aclutch pedal. While some designs for clutches are known that permit anelectrical current to directly effect coupling and uncoupling of theclutch, such clutches generally consume, and must therefore alsodissipate, a significant amount of electrical power. Thus, even withmicroprocessor controlled operation of an automotive vehicle'stransmission, it still appears desirable to continue controlling clutchoperation indirectly by converting a control electrical signal from themicroprocessor into a more powerful mechanical driving force fordirectly operating a conventional clutch.

In pursuing this indirect electronic control of automotive vehicleclutches, some automotive vehicle manufacturers have chosen to employelectro-hydraulic transmissions having hydraulically operated clutches.In such electro-hydraulic transmissions, a hydraulic pump suppliespressurized hydraulic fluid for energizing a hydraulic actuator, forexample a piston or a bellows, that directly operates the clutch. In onedesign for such a clutch, springs hold the clutch in its disengagedposition and a carefully controlled pressure of the hydraulic fluid fromthe pump overcomes the springs' force to effect engagement of theclutch. When the hydraulic pressure is removed from this clutch, thesprings once again move the clutch into its disengaged state. By usingthe spring pressure to effect clutch disengagement and hydraulicpressure to effect clutch engagement, the clutch inherently disconnectsthe engine from the transmission when the engine is not running to powerthe hydraulic fluid pump. Furthermore, this method of operating anelectro-hydraulic clutch inherently avoids creating a hazardouscondition if the hydraulic fluid pump fails. With such anelectro-hydraulically operated clutch, smoothly accelerating the vehicleinto motion and smoothly shifting transmission gear ratios require ahydraulic valve that controls the pressure of the hydraulic fluidsupplied to the clutch precisely in response to changing values of thecontrolling electrical signal.

U.S. Pat. No. 4,996,195 entitled “Transmission Pressure Regulator”issued on Oct. 30, 1990 to Ralph P. McCabe (“the McCabe patent”) anddiscloses a valve for controlling the pressure of a fluid medium that isadapted for use in a control system such as that of an automatictransmission of an automotive vehicle.

The valve disclosed in the McCabe patent includes a cylindricallyshaped, elongated, hollow aperture means or cage. Formed through thewall of the cage toward one end is a first set of apertures or ports.This first set of ports receives a supply pressure of hydraulic fluid,apparently from a pump (not depicted or described in the text ordrawings of the McCabe patent). A second set of apertures or ports alsopasses through the wall of the aperture means or cage. The second set ofports is displaced laterally from the first set of ports along thelength of the cage and located near the middle of the length of thecage. The hydraulic fluid in the second set of ports has a controlpressure and, apparently, is supplied to the automatic transmission (notdepicted or described in the McCabe patent). A third set of apertures orports is formed in the wall of the cage. The third set of ports isdisplaced laterally along the length of the cage from both the first andsecond sets of ports and is located near the end of the cage furthestfrom the first set. The hydraulic fluid in this third set of ports has asump or tank pressure, and appears to return from the valve to a tank(not depicted or described in the McCabe patent).

The inner surface of the cage is formed in the shape of a right,circular cylinder and receives a snugly fitting main spool. The spool ismuch shorter than the cage and can, therefore, move laterally back andforth within the cage while remaining totally enclosed therein. A broadtrough encircles the outer surface of the spool about its mid-section toestablish a first chamber between the outer surface of the spool and theinner surface of the cage. The width of this trough along the length ofthe spool permits the first chamber to couple immediately adjacent pairsof sets of ports to each other while not simultaneously coupling allthree sets of ports to each other. As depicted in FIGS. 1 and 2 of theMcCabe patent, when the spool is fully displaced toward the right, thefirst chamber couples the second set of apertures, i.e., the clutchports, to the third set of apertures, i.e., the tank ports.Alternatively, when the spool is fully displaced toward the left, thefirst chamber couples the first set of apertures, i.e., the pump ports,to the second set of apertures, i.e., the clutch ports. Thus, preciselycontrolled motion of the main spool laterally within the cage couplesthe set of clutch ports either to the set of pump ports ox to the set oftank ports, and, as described in the McCabe patent, can thereby controlthe hydraulic fluid pressure in the clutch ports.

As depicted in FIGS. 1 and 2 of the McCabe patent, the outer surface ofthe spool is also encircled by a narrow trough located near its leftend. This narrow trough establishes a second chamber between the outersurface of the spool and the inner surface of the cage. The secondchamber appears to be always open to a flow of hydraulic fluid from thepump through the pump ports through the wall of the cage.

Located in the interior of the spool disclosed in the McCabe patent is ahollow first internal passage. The formation of this passage in thespool establishes a cup-shaped cavity that is open toward the right endof the spool and closed at the spool's left end. A passage, formedthrough the wall of the spool, connects this cup-shaped cavity to thesecond chamber. From FIGS. 1 and 2 of the McCabe patent, it appears thatthe first internal passage in the spool always receives a flow ofhydraulic fluid from the pump through the pump ports in the cage and thesecond chamber regardless of the lateral position of the spool along thelength of the cage.

The spool disclosed in the McCabe patent also includes a second internalpassage that pierces both the wall of the broad trough and the left endsurface of the spool. This second internal passage couples the pressureof hydraulic fluid in the first chamber to a second cavity located atthe left end of the spool between the spool and an end cap. The end capcloses the end of the cage to the left of the spool and seals the secondcavity so that fluid may enter and leave it only through the secondinternal passage. Because the second cavity opens only into the secondinternal passage, the pressure within this second cavity always equalsthe pressure of fluid within the first chamber. The end cap alsocompresses a first coil spring between its inner surface and the lefthand surface of the spool. In the absence of any other force on thespool, this first coil spring urges the spool toward the right end ofthe cage as depicted in FIGS. 1 and 2 of the McCabe patent.

An annularly shaped poppet valve plate is located immediately to theright of the spool as depicted in FIGS. 1 and 2 of the McCabe patent,and partially obscures the right hand end of the cylindrically shapedinterior of the cage. The full pressure of hydraulic fluid applied bythe pump to the pump ports forces hydraulic fluid through the pump portsin the wall of the cage, the second chamber, and the first internalpassage in the spool to the side of the poppet plate immediatelyadjacent to the right hand end of the spool. A second coil spring iscompressed between the spool and the poppet plate at the right end ofthe spool and, according to the text of the McCabe patent, applies aforce to the spool that is smaller than that applied by the first coilspring at the left end of the spool.

Located to the right of the poppet plate is a movable armature that issurrounded by a solenoid coil. An electrical current flowing through thecoil applies a magnetic force to the armature. In the valve depicted inFIG. 1 of the McCabe patent, this electromagnetic force on the armatureurges it to move laterally toward the left which tends to close theopening in the center of the annularly shaped poppet valve.

According to the text of the McCabe patent, closure of the poppet valveincreases the pressure of the hydraulic fluid at the right end of thespool adjacent to the poppet plate. With the spool urged to the rightend of the cage by the first coil spring, an increase in hydraulic fluidpressure on the right end of the spool urges it to move laterally to theleft away from the poppet plate. Movement of the spool to the leftcauses the first chamber to move laterally away from the tank portstoward the pump ports. Lateral movement of the first chamber over thepump ports permits hydraulic fluid to flow from the pump ports to theclutch ports thereby increasing the pressure of the hydraulic fluid inthe clutch ports. Increased pressure of the hydraulic fluid in theclutch ports is coupled via the second internal passage to the secondcavity thereby increasing the pressure of the hydraulic fluid in thesecond cavity at the left end of the spool. An increasing pressure inthe second cavity urges the spool to halt its lateral movement to theleft away from the poppet plate and urges it to begin moving back to theright toward the poppet plate. According to the text of the McCabepatent, “the spool . . . will move axially in relation to the poppetplate . . . until the sum of the forces on the spool . . . are inequilibrium.” The text of the McCabe patent also states that the secondcoil spring compressed between the poppet plate and the spool acts toreduce lateral oscillation of the spool due to changes in the pressureof hydraulic fluid at opposite ends of the spool. Thus, according to theMcCabe patent, the combination of the poppet valve at the right end ofthe spool with the second internal passage in the spool and the secondcavity at the left end of the spool along with the second coil spring,precisely controls the movement of the main spool laterally within thecage to adjust the pressure in the clutch ports.

Based upon the preceding description of the operation of the valvedepicted in FIG. 1 of the McCabe patent, that valve may be characterizedas a normally closed valve that couples the clutch ports to the tankports when no current flows through the coil. Conversely, the valvedepicted in FIG. 2 of the McCabe patent includes a spring which biasesthe poppet valve closed, and a magnetic field generated by an electriccurrent flowing through the toil urges the armature to move toward theright thereby opening the poppet valve. According to the text of theMcCabe patent, the hydraulic pressure applied to the right end of thespool of the valve depicted in FIG. 2 when no current flows through thecoil causes the spool to move to the left thereby causing the firstchamber to couple the clutch ports to the pump ports. Thus the valveembodiment depicted in FIG. 2 of the McCabe patent may be characterizedas a normally open valve that couples the clutch ports to the pump portswhen no current flows through the coil.

The text of the McCabe patent appears to lack an explanation of howclosing and opening of the poppet valve depicted in the drawings of thepatent may increase or decrease the pressure of hydraulic fluid presentat the right end of the spool adjacent to the annularly shaped poppetplate. Accordingly, it appears that the valve disclosed in the McCabepatent may be commercially impractical for its intended purpose ofcontrolling the pressure of hydraulic fluid in an automatic transmissionof an automotive vehicle.

U.S. Pat. No. 4,996,195 entitled “Pilot-Operated Valve With LoadPressure Feedback” issued on May 3, 1988 to Kenneth J. Stoss and RichardA Felland (“the Stoss et al. patent”) discloses a pilot-operatedelectro-hydraulic valve adapted for use in controlling a transmission ofan automotive vehicle. The valve disclosed in the stoss et al. patentincludes an electromagnetically controlled pilot valve that controls theoperation of the valve's main spool. A pilot feedback passage couplesthe pressure of hydraulic fluid in the load or clutch port of the valveto a feedback chamber at one end of the pilot valve. The Stoss et al.patent discloses that a pilot feedback passage coupling the clutch portto the feedback chamber preferably includes a filtered orifice. TheStoss et al. patent appears to omit an explanation of the functionprovided by the filtered orifice.

Neither the McCabe patent nor the Stoss et al. patent disclose or solvea problem that occurs in the operation of clutches in electro-hydraulictransmissions known as spiking. Spiking is a phenomenon that resultsfrom abruptly halting fluid flow through a hydraulic system. Fluidflowing through a hydraulic system has two types of energy. Those twodifferent types of energy are potential energy and kinetic energy.Potential energy is energy that is present due to the pressure ofhydraulic fluid. Kinetic energy is energy that is present due to theflow of fluid through the hydraulic system.

When a clutch, or any other hydraulically operated device that is movingin response to a flow of hydraulic fluid reaches the mechanical limit ofits travel, the hydraulic fluid flow through the system stops abruptly.This abrupt stopping of hydraulic fluid flaw converts the fluid'skinetic energy into potential energy thereby producing a sudden andabnormal increase, or spike, in the pressure of the hydraulic fluid.Under appropriate circumstances, this pressure spike may be heardaudibly as a disturbing or alarming noise, and the pressure increase maybe so severe that it causes failure of the hydraulic system.

SUMMARY OF THE INVENTION

The present invention provides a commercially practical electricallyenergized, hydraulic proportional pressure control valve for use inelectro-hydraulic transmissions having hydraulically operated clutches.

An object of the present invention is to provide a fully operableelectrically energized, hydraulic proportional pressure control valvefor use in electro-hydraulic transmissions.

Another object of the present invention is to provide an electricallyenergized, hydraulic proportional pressure control valve that controlsthe pressure in its clutch port precisely in response to changing valuesof the controlling electrical signal.

Yet another object of the present invention is to provide anelectrically energized, hydraulic proportional pressure control valvethat relieves the abnormally high hydraulic fluid pressure spike thatoccurs when a flow of hydraulic fluid through the valve stops abruptly.

Another object of the present invention is to provide an electricallyenergized, hydraulic proportional pressure control valve that reducesthe abnormally high hydraulic fluid pressure spike, that occurs when aflow of hydraulic fluid through the valve stops abruptly.

Another object of the present invention is to provide a simplerelectrically energized, hydraulic proportional pressure control valve.

Another object of the present invention is to provide a more easilymanufactured electrically energized, hydraulic proportional pressurecontrol valve.

Another object of the present invention is to provide a more economicalelectrically energized, hydraulic proportional pressure control valve.

Another object of the present invention is to provide an electricallyenergized, proportional pressure control valve that, when used inconjunction with a clutch, provides improved and smooth engagement anddisengagement of a load through precise control of fluid pressureswithin a hydraulic system.

A further object of the present invention is to provide an electricallyenergized, proportional pressure control valve that has an improvedpilot valve section alloying precise control of fluid pressures within ahydraulic system.

Another object of the invention is to provide an electrically energized,proportional pressure control valve that has an improved ball type pilotvalve section which allows precise control of fluid pressures within ahydraulic system and substantially reduces the cost of such a valve.

A further object of the invention is to provide an electronicallyenergized, proportional pressure control valve that includes improvedfeedback means to dampen oscillation within the valve.

Briefly a proportional pressure control valve in accordance with thepresent invention includes a hollow cage having a wall that is piercedby a pump port, by a clutch port, and by a tank port. The pump portreceives hydraulic fluid from a pump at a pressure provided by the pump.The clutch port is adapted for supplying pressurized hydraulic fluid toa hydraulic actuator at a pressure that is controlled by theproportional pressure control valve. The tank port of the cage returnshydraulic fluid from the proportional pressure control valve to a tankfrom which the fluid circulates back to the pump.

The proportional pressure control valve also includes a main spooladapted to fit snugly within the cage. Contained within the cage, themain spool is movable along the length of the cage for controlling aflow of hydraulic fluid passing between the clutch port and either thepump port or the tank port.

An electromagnetically operated pilot valve regulates a control pressureof hydraulic fluid that is present in a control pressure chamber of theproportional pressure control valve. The pressure of the fluid in thecontrol pressure chamber is applied to a control pressure surface of themain spool. Pressure applied to the control pressure surface urges themain spool to move along the length of the cage to a position in whichit allows hydraulic fluid to flow between the pump port and the clutchport. When disposed in such a position, the main spool obstructs anyflow of hydraulic fluid between the clutch port and the tank port.

A feedback pressure passage couples the pressure of hydraulic fluid inthe clutch port of the proportional pressure control valve to a feedbackpressure chamber. The feedback pressure chamber applies the pressure ofhydraulic fluid in the clutch port to a feedback surface of the mainspool. Pressure applied to the feedback pressure surface of the mainspool urges the main spool to move within the cage to a position inwhich it allows a flow of hydraulic fluid to pass between the clutchport and the tank port. When disposed in such a position, the main spoolobstructs any flow of hydraulic fluid between the pump port and theclutch port. The feedback pressure passage includes a feedbackrestriction orifice for restraining the rate at which fluid may flowbetween the clutch port and the feedback pressure chamber.

An embodiment of the proportional pressure control valve of the presentinvention includes a pressure spike suppression check valve forrelieving any abnormally high pressure that occurs in the clutch port ofthe cage. Such an abnormally high pressure may occur if a flow ofhydraulic fluid through the clutch port stops abruptly. In the preferredform of this embodiment, the check valve allows hydraulic fluid to flowfrom the cage clutch port to the cage tank port when an abnormally highpressure occurs in the clutch port. A spike suppression orifice may alsobe included to restrain the rate at which fluid may flow through thecheck valve.

These and other features, objects and advantages will be understood orapparent to those of ordinary skill in the art from the followingdetailed description of the preferred embodiment as illustrated in thevarious drawing figures.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1, made up of FIGS. 1A and 1B, is an exploded, cross-sectional planview of a normally closed proportional pressure control valveconstructed in accordance with the present invention that is adapted forcontrol by an analog electrical control signal;

FIG. 2 is a cross-sectional plan view of the assembled proportionalpressure control valve depicted in FIG. 1;

FIG. 3 is a plan view of a plunger included in the proportional pressurecontrol valve depicted in FIGS. 1 and 2 taken along the line 3—3 in FIG.1;

FIG. 4A through 4D are cross-sectional plan views of a portion of theassembled proportional pressure control valve of FIGS. 1 and 2illustrating motion of the main spool relative to the cage;

FIG. 5, made up of FIGS. 5A and 5B, is an exploded, cross sectional planview of a normally open proportional pressure control valve inaccordance with the present invention that is adapted for control by adigital electrical control signal;

FIG. 6 is a cross-sectional plan view of the assembled proportionalpressure control valve depicted in FIG. 5;

FIG. 7, made up of FIGS. 7A and 7B, is an exploded, cross sectional planview of a normally closed proportional pressure control valve inaccordance with the present invention that is adapted for control by adigital electrical control signal;

FIG. 8 is a cross-sectional plan view of the assembled proportionalpressure control valve depicted in FIG. 7; and

FIG. 9 is a cross-sectional plan view of a spool in accordance with thepresent invention including a pressure spike suppression check valve forrelieving any abnormally high pressure that occurs in the clutch port ofthe cage;

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 depicts a cross-sectional plan view of a normally closedproportional pressure control valve referred to by the general referencecharacter 20. FIG, 1, made up of FIGS. 1A and 1B, is an exploded,crass-sectional plan view depicting the various parts included in theproportional pressure control valve 20. The same reference charactersare used to identify the some part of the proportional pressure controlvalve 20 both in FIG. 1 and in FIG. 2.

The proportional pressure control valve 20 includes a body 22. Formed inthe center of the body 22, symmetrically about a center line 24 thatappears only in FIG. 1, is a cylindrically shaped cavity 26. Surroundingthe cavity 26 is a body wall 28 that is pierced by a body tank port 32and a body clutch port 34. During normal operation of the proportionalpressure control valve 20, the pressure of hydraulic fluid in the bodytank port 32 is very low because the body tank port 32 connects to anunpressurized hydraulic fluid reservoir (not depicted in any of theFIGS.).

The cavity 26 is formed to receive a cylindrically-shaped, elongated,hollow cage 42 having a cylindrically-shaped cage wall 44. Formedthrough the cage wall 44, toward one end of the cage 42, is a set ofcage tank ports 52. Displaced laterally along the length of the cage 42from the cage tank ports 52 and locates approximately about the middleof the cage 42 is a set of cage clutch ports 54 that pass through thecage wall 44. Displaced even further laterally along the length of thecage 42 from the cage tank ports 52 than the cage clutch ports 54 is aset of cage pump ports 56 that also pass through the cage wall 44. Thecage wall 44 between the cage tank ports 52 and the cage clutch ports 54includes a pair of raised lands 62 that encircle the cage 42. The lands62 establish a U-shaped trough 64 that also encircles the cage 42 andreceives an encircling O-ring 66. Similarly, the cage wall 44 betweenthe cage clutch ports 54 and the cage pump ports 56 includes anotherpair of raised lands 72 that encircle the cage 42. The lands 72establish another U-shaped trough 74 that encircles the cage 42 andreceives another encircling O-ring 76.

When the cage 42 is inserted into the cavity 26 in the body 22, thesurface of the cavity 26 receives the raised outer surface of the lands62 and 72, and the O-rings 66 and 76 seal between the surface of thecavity 26 and the outer surface of the cage wall 44. With the cage 42disposed in this position within the body 22, the surface of the cavity26 and the outer surface of the cage wall 44 between immediatelyadjacent lands 62 and 72 established a hollow, annularly-shaped clutchoutlet chamber 82 that encircles the cage 42. Hydraulic fluid, that isapplied to a hydraulic actuator (not depicted in any of the FIGS. ),flows between the cage clutch ports 54 and the body clutch port 34through the clutch outlet chamber 82. On the opposite side of the lands72 from the clutch outlet chamber 82, the surface of the cavity 26 andthe outer surface of the cage wall 44 establish a hollow,annularly-shaped pump inlet chamber 84 that also encircles the cage 42.The pump inlet chamber 84 receives pressurized hydraulic fluid from apump (not depicted in any of the FIGS.) and supplies it to the interiorof the cage 42 through the cage pump ports 56.

A cup-shaped plug 92 fits snugly within the interior surface of the cagewall 44 at the end of the cage 42 nearest the cage pump ports 56. AU-shaped trough 94 encircles the plug 92 and receives an O-ring 96. TheO-ring 96 seals between the inner surface of the cage wall 44 and theouter surface of the plug 92. The inner surface of the cage wall 44immediately adjacent to the plug 92 includes a U-shaped groove 102. Thegroove 102 receives a snap ring 104 that mechanically retains the plug92 within the cage 42. Secured in this location, the plug 92 closes theinterior surface of the cage 42 between the plug 92 and the cage pumpports 56 formed through the cage wall 44. Received within the cage 42abutting the plug 92 is a coil spring 108.

The inner surface of the cage wall 44 is formed in the shape of a right,circular cylinder to receive a snugly fitting main spool 112. While thelength of the main spool 112 is shorter than that of the cage 42, themain spool 112 nevertheless abuts the end of the coil spring 108furthest from the plug 92 to compress the coil spring lO8 between theplug 92 and a feedback pressure surface 114 of the main spool 112. Thepressure of the coil spring 108 against the feedback pressure surface114 urges the main spool 112 to move laterally along the length of thecage 42 away from the plug 92.

When the main spool 112 is properly disposed within the cage 42, theplug 92, the feedback pressure surface 114 of the main spool 112, andthe interior surface of the cage wall 44 between the plug 92 and thefeedback pressure surface 114 establish a feedback pressure chamber 118.In addition to the coil spring 108, any hydraulic fluid pressure within-the feedback pressure chamber 118 also urges the main spool 112 to movelaterally along the length of the cage 42 away from the plug 92.

A broad, U-shaped trough 122 encircles the outer surface of the mainspool 112 about its mid-section. When the main spool 112 is properlydisposed within the cage 42, the outer surface of the main spool 112formed by the trough 122 and the inner surface of the cage wall 44establish a hollow, annularly-shaped valuing chamber 124 that encirclesthe main spool 112. A sufficiently large lateral movement of the mainspool 112 toward the plug 92 allows hydraulic fluid to flow throughvaluing chamber 124 between the cage pump ports 56 and the cage clutchports 54 while the outer surface of the main spool 112 simultaneouslyobscures the cage tank ports 52 thereby obstructing hydraulic fluid flowthrough the cage tank ports 52. Alternatively, a sufficiently largelateral movement of the main spool 112 away from the plug 92 allowshydraulic fluid to flow through the valuing chamber 124 between the cageclutch ports 54 and the cage tank ports 52 while the outer surface ofthe main spool 112 simultaneously blocks any substantial flow ofhydraulic fluid between the cage pump ports 56 and the cage clutch ports54. Thus, controlled movement of the main spool 112 laterally along thelength of the cage 42 couples the cage clutch ports 54 either to thecage pump ports 56 or to the cage tank ports 52.

A feedback pressure passage 126 is formed into the end of the main spool112 adjacent to the coil spring 108 and the plug 92. A feedbackrestriction orifice 128, formed at the end of the feedback pressurepassage 126 furthest from the coil spring 108 and the plug 92, passesthrough the surface of the trough 122 thereby coupling the feedbackpressure passage 126 to valving chamber 124. Because the cage clutchports 54 always open into the valving chamber 124, the feedback pressurepassage 126 continuously couples the pressure of hydraulic fluid in thecage clutch ports 54 through the main spool 112 to establish a feedbackpressure for the hydraulic fluid within the feedback pressure chamber118. The feedback restriction orifice 128 in the feedback pressurepassage 126 restrains the rate at which hydraulic fluid may flow betweenthe valving chamber 124 and the feedback pressure chamber 118. Thefeedback restriction orifice 128 is sized dependant upon flow rate offluid within the system as well as the size of the main spool 112 toprovide acceptable overshoot spike suppression and operational stabilityof the system. To accomplish these intended purposes, feedbackrestriction orifice 128 is approximately about .020″ to about .040″indiameter.

The outer surface of the main spool 112 between the trough 122 and thefeedback pressure surface 114 is also encircled by a narrow trough 132.This narrow trough 132 establishes a hollow, annularly-shaped pilotvalve supply chamber 134 encircling the main spool 112 between the outersurface of the main spool 112 and the inner surface of the cage wall 44.Regardless of the lateral position of the main spool 112 along thelength of the cage 42, the pilot valve supply chamber 134 is always opento a flow of hydraulic fluid from the pump through the cage pump ports56 in the cage wail 44. One end of a pilot valve supply passage 136,formed through the interior of the main spool 112, is open to the trough132 while the other end of the pilot valve supply passage 136 passesthrough a control pressure surface 138 on the outer surface of the mainspool 112 furthest from the coil spring 108 and the plug 92. In theproportional pressure control valve 20 depicted in FIGS. 1 and 2, thepilot valve supply passage 136 immediately adjacent to the controlpressure surface 138 receives a, screen 142 and is threaded to receive athreaded control flow restriction orifice 144. The control flowrestriction orifice 744 restrains the flow rate of a control pressureflow of hydraulic fluid that passes from the cage pump ports 56 throughthe trough 132, the pilot valve supply passage 136, and through thecontrol pressure surface 138 of the main spool 112. The screen 142catches particles in the hydraulic fluid to hinder blockage of thecontrol flow restriction orifice 144 by such particles.

An annularly-shaped stop 152 fits snugly within the interior surface ofthe cage wall 44 at the end of the cage 42 nearest the cage tank ports52. A U-shaped trough 154 encircles the stop 152 and receives an O-ring156. The O-ring 156 seals between the inner surface of the cage wall 44and the outer surface of the stop 152. When the main spool 112 isproperly disposed within the cage 42, the stop 152, the control flowrestriction orifice 144, the control pressure surface 138 of the mainspool 112, and the interior surface of the cage wall 44 between the stop152 and the control pressure surface 138 establish a control pressurechamber 158. The pressure of hydraulic fluid within the control pressurechamber 158 urges the main spool 112 to move laterally along the lengthof the cage 42 away from the stop 152 toward the plug 92.

Passing through the middle of the stop 152 is a hollow control pressurechamber outlet passage 162. Formed on the edge of the control pressurechamber outlet passage 162 furthest from the control pressure surface138 of the main spool 112 is a beveled valve seat 164.

Formed on the outer surface of the cage wall 44 surrounding the stop 152are threads 172 adapted to mate with threads 174 formed on the interiorsurface of an annularly-shaped adaptor 176 of a tube assembly 178.Formed on the outer surface of the adaptor 176 are threads 182 adaptedto mate with threads 184 formed at one end of the cavity 26 formed inthe body 22. A U-shaped trough 186 encircles the adaptor 176 immediatelyadjacent to the threads 182 and receives an encircling 0-ring 188. TheO-ring 188 seals between the outer surface of the adaptor 176 and thesurface of the cavity 26 in the body 22. With the adaptor 176 disposedin this position within the body 22 and mated with the cage 42, thesurface of the cavity 26, the end surface of the adaptor 176, the outersurface of the cage wall 44 and the land 72 nearest to the adaptor 176establish a hollow, annularly-shaped tank outlet chamber 192 encirclingthe cage 42. Hydraulic fluid flowing to the tank flows between the cagetank ports 52 and the body tank port 32 through the tank outlet chamber192.

A pair of control pressure flow return ports 194 pass through theadaptor 176 at the end of the threads 174 and 182 immediately adjacentto the trough 186 and the O-ring 188. A pair of elongated controlpressure flow return slots 196 extend across the threads 182 from thecontrol pressure flow return ports 194 away from the trough 186 and theO-ring 188. The control pressure flow return ports 194 and the controlpressure flow return slots 196 provide a passage by which the controlpressure flow of hydraulic fluid, that flows out of the control pressurechamber 158 through the control pressure chamber outlet passage 162,returns to the body tank port 32 and the cage tank ports 52, and thenceto the tank.

Projecting outward from the side of the annularly-shaped adaptor 176opposite to the threads 174 and 182 is a hollow tube 202 included in thetube assembly 178. The tube 202 is rigidly attached to the adaptor 176and sealed to it. Also rigidly attached and sealed to the tube 202 atits end furthest from the adaptor 176 is an annularly-shaped threadedtube plug 204 also included in the tube assembly 178.

Received within the adaptor 176 and positioned at the end of the tube202 nearest the adaptor 176 is an elongated, annularly-shaped pole piece212. A raised land 214 encircles the outer surface of the pole piece212. When the adaptor 176 is threaded onto the cage 42, the adaptor 176presses the land 214 against the stop 152. Thus, threading the adaptor176 onto the cage 42 forces the stop 152 into the cage 42 and holds itthere. An annularly-shaped recess 216 is formed into the end of the polepiece 212 immediately adjacent to the stop 152. A pair of elongatedslots 218 are formed along the entire length of the pole piece 212 andacross the land 214 to open into the recess 216. The recess 216 and theends of the slots 218 crossing the land 214 also form part of thepassage by which the control pressure flow of hydraulic fluid, thatflows out of the control pressure chamber 158 through the controlpressure chamber outlet passage 162, returns to the body tank port 32and cage tank ports 52, and thence to the tank. The slots 218 allowhydraulic fluid to flow past the pole piece 212 and fill the length ofthe tube 202 extending outward from the adaptor 176.

Formed through the middle of the pole piece 212 is an elongated,cylindrically-shaped pin passage 222. An elongated pin 224 fits looselywithin the pin passage 222 and slides freely back and forth within thelength of the pin passage 222. The end of the pin passage 222immediately adjacent to the recess 216 is formed with an enlargeddiameter to provide a valve ball retaining chamber 226. The valve ballretaining chamber 226 receives a loosely fitting valve ball 228 that isfree to move back and forth along the length of the valve ball retainingchamber 226. Within the proportional pressure control valve 20, thevalve ball retaining chamber 226 supports the valve ball 228 in aposition in which the pin 224 may urge the valve ball 228 into sealingengagement with the valve seat 164 of the stop 152.

Loosely received within the tube 202 of the tube assembly 178 betweenthe pole piece 212 and the threaded tube plug 204 is a plunger 232. Theplunger 232 is free to move back and forth within the tube 202 betweenthe pole piece 212 and the threaded tube plug 204. The end of theplunger 232 nearest the pole piece 212 contacts the end of the pin 224that extends out of the pole piece 212 furthest from the valve ball 228.A spring cavity 234 is formed into the end of the plunger 232 nearestthe threaded tube plug 204 to receive a light, minimum pressure coilspring 236. A partially threaded, central passage 238, that passeslongitudinally through the middle of the threaded tube plug 204,receives the end of the spring 236 that projects out of the end of theplunger 232. As illustrated in the plan view of FIG. 3, the outersurface of the plunger 232 parallel to the center line 24 is not formedin the shape of a full right circular cylinder. Rather, portions of theouter surface of the plunger 232 parallel to the center line 24 areformed by planar surfaces 240.

A preload adjusting screw 242 threads into the central passage 238 andcontacts the end of the spring 236 within the central passage 238.Threading the preload adjusting screw 242 into the central passage 238of the threaded tube plug 204 presses the spring 236 into the springcavity 234 of the plunger 232. This force on the plunger 232 urges itinto contact with the immediately adjacent end of the pin 224 whose farend contacts the valve ball 228. This force applied to the valve ball228 by the preload adjusting screw 242 urges the valve ball 228 into asealing contact with the valve seat 164 of the stop 152.

A U-shaped trough 244 encircles the end of the preload adjusting screw242 nearest the spring 236 and receives an O-ring 246. The O-ring 246seals between the threaded tube plug 204 and the preload adjusting screw242 to close the end of the tube assembly 178 furthest from the body 22.Because the tube assembly 178 is formed as a sealed unit, because theO-ring 246 seals between the preload adjusting screw 242 and thethreaded tube plug 204, and because the O-ring 188 seals between theadaptor 176 and the body 22, hydraulic fluid normally enters theproportional pressure control valve 20 only through the pump inletchamber 84 and normally leaves the proportional pressure control valve20 only through the body tank port 32 and the body clutch port 34.

The proportional pressure control valve 20 also includes anannularly-shaped solenoid coil 252 that loosely encircles the tube 202of the tube assembly 178 immediately adjacent to the adaptor 176. Anannularly-shaped spacer 254 also loosely encircles the tube 202 of thetube assembly 178 on side of the solenoid coil 252 furthest from theadaptor 176. A flux ring 253 is located between the coil shell and theadaptor 176 to enhance magnetic flux between the coil and the adaptor. Anut 256 threads onto the threaded tube plug 204 to contact the spacer254 thereby urging it along the length of the tube assembly 178 towardthe adaptor 176. Thus, force from the nut 256 holds the solenoid coil252 in contact with the adaptor 176. The solenoid coil 252 includes apair of electrically conductive leads 258. Applying an electricalcontrol signal to the leads 258 produces a magnetic field within thetube 202 of the tube assembly 178. This magnetic field applies a forcethat pushes the plunger 232 along the length of the tube 202 toward thevalve ball 228. Thus, in addition to the coil spring 236, an electriccurrent flowing through the solenoid coil 252 also applies a force tothe valve ball 228 that urges it into a sealing contact with the valveseat 164 of the stop 152.

With no electric current passing through the solenoid coil 252 of theproportional pressure control valve 20 depicted in FIGS. 1 and 2, thepressure of the hydraulic fluid supplied by the pump to the pump inletchamber 84 is transmitted substantially undiminished to the control flowrestriction orifice 144 retained in the main spool 112. The controlpressure flow of hydraulic fluid passing through the control flowrestriction orifice 144 fills the control pressure chamber 158 and flowsout of the control pressure chamber 158 through the control pressurechamber outlet passage 162. This control pressure flow of fluid throughthe control pressure chamber outlet passage 162 impinges upon the valveball 228 urging it away from the valve seat 164 on the stop 152. Thepressure applied to the plunger 232 by the spring 236 applies only alight force urging the valve ball 228 back toward the valve seat 164.Therefore, when no electrical current passes through the solenoid coil252, it requires only a low pressure for fluid within the controlpressure chamber 158 to overcome the force applied to the valve ball 228by the coil spring 236 and to push the valve ball 228 away from the stop152.

With the valve ball 228 thus displaced away from the valve seat 164against only the force applied by the spring 236, the control flowrestriction orifice 144 located within the main spool 112 restrains theflow rate of the control pressure flow of hydraulic fluid passingthrough the pilot valve supply passage 136 to a low value. Theresistance to this low rate of fluid flow past the valve ball 228 andthrough the control pressure flow return passage to the cage tank ports52 provides a back up pressure that is sufficiently low such that littleforce is applied by the fluid in the control pressure chamber 158 to thecontrol pressure surface 138 of the main spool 112. Therefore, the forceapplied to the feedback pressure surface 114 of the main spool 112 bythe coil spring 108 within the feedback pressure chamber 118 pushes themain spool 112 toward the stop 152.

In the proportional pressure control valve 20 depicted in FIGS. 1 and 2,varying the pressure applied to the plunger 232 by the spring 236adjusts the hydraulic fluid pressure present in the cage clutch ports 54of the cage 42 to a predetermined pressure valve. This is accomplishedby turning the preload adjusting screw 242 within the threaded tube plug204.

The coil spring 236, the central passage 238 in the plug 204 and theadjustable screw 242 may be eliminated in applications where back-uppressure is not required or is undesirable. Such an arrangement isillustrated in FIG. 6 and described below.

When the control pressure surface 138 of the main spool 112 is locatedimmediately adjacent to the stop 152, the main spool 112 spool blockssubstantially all fluid flow through the cage pump ports 56 to the cageclutch ports 54 while the valuing chamber 124 allows fluid to flowfreely from the cage clutch ports 54 to the cage tank ports 52. Becausethe valuing chamber 124 couples the cage clutch ports 54 to the cagetank ports 52, substantially the same low pressure of hydraulic fluid ispresent both in the body tank port 32 and in the body clutch port 34.

Applying an electrical control signal to the leads 258 increases theforce pushing the plunger 232 toward the stop 152. This increased forceon the plunger 232 is applied by the pin 224 to the valve ball 228. Theforce from the plunger 232 urges the valve ball 228 toward the valveseat 164 thereby reducing the control pressure flow of fluid out of thecontrol pressure chamber outlet passage 162 and increasing the pressureof fluid within the control pressure chamber 158. The increased fluidpressure within the control pressure chamber 158 presses against thecontrol pressure surface 138, overcomes the force applied to the mainspool 112 by the coil spring 108 located in the feedback pressurechamber 118, and moves the main spool 112 away from the stop 152 towardthe plug 92 as illustrated in FIGS. 4A through 4D. Movement of the mainspool 112 away from the stop 152 first causes the outer surface of themain spool 112 to occlude the cage tank ports 52 and then allows thevaluing chamber 124 to couple the cage clutch ports 54 to the cage pumpports 56. Coupling of the cage clutch ports 54 to the cage pump parts 56increases the pressure of hydraulic fluid within the body clutch port34.

The increased pressure of fluid in the body clutch port 34 is coupledthrough the cage clutch ports 54, the valuing chamber 124, feedbackrestriction orifice 128, and the feedback pressure passage 126 to thefeedback pressure chamber 118. The pressure of fluid in the feedbackpressure chamber 118 presses against the feedback pressure surface 114of the main spool 112 to oppose the force applied to the controlpressure surface 138 of the main spool 112 by the fluid in the controlpressure chamber 158. When the forces applied to these opposite ends ofthe main spool 112 become equal the main spool 112 stops moving withinthe cage 42 and the proportional pressure control valve 20 maintains aconstant fluid pressure within the body clutch port 34. Any inequalitybetween the forces applied simultaneously to the control pressuresurface 138 and to the feedback pressure surface 114 of the main spool112 cause the main spool 112 to move laterally within the cage 42. Inresponse to such unequal forces, the main spool 112 moves away from theend receiving the larger force and toward the end receiving the lesserforce. Because the feedback restriction orifice 128 restrains the rateat which hydraulic fluid may flow from the valving chamber 124 to thefeedback pressure chamber 118, it dampens out possible oscillation ofthe main spool 112 within the cage 42. Operated in this manner, thesolenoid coil 252, the plunger 232, the pin 224, the valve ball 228, thestop 152, and the control flow restriction orifice 144 provide anelectromagnetically operated pilot valve for supplying a regulatedpressure of fluid to the control pressure chamber 158 responsive to anelectrical control signal.

Changing the electrical control signal so an electrical current nolonger flows through the solenoid coil 252 again permits the fluidpressure from the cage pump ports 56 to overcome the force applied tothe valve ball 228 and move it away from the valve seat 164 on the stop152. Moving the valve ball 228 away from the valve seat 164 reduces theforce applied to the control pressure surface 138 of the main spool 112by fluid pressure within the control pressure chamber 158. With a lesserforce being applied to the control pressure surface 138, both the forceapplied to the feedback pressure surface 114 by the coil spring 108 andany residual pressure in the feedback pressure chamber 118 urge thespool to move back toward the stop 152.

Applying different levels of electrical control signals providesdifferent solenoid forces and therefore different pressures in thecontrol chamber and the clutch in proportion to electric signals. Thistype of signal control makes proportional pressure control andcorresponding clutch torque control possible.

FIG. 6 depicts a cross-sectional plan view of a proportional pressurecontrol valve referred to by the general reference character 310. FIG.5, made up of FIGS. 5A and 5B, is an exploded, cross-sectional plan viewdepicting the various parts included in the proportional pressurecontrol valve 310. Those elements depicted in FIGS. 5 and 6 that arecommon to the proportional pressure control valve 20 depicted in FIGS. 1and 2 carry the same reference numeral distinguished by a prime (“′”)designation. The same reference characters are used to identify the samepart of the proportional pressure control valve 310 both in FIG. 5 andin FIG. 6. The proportional pressure control valve 310 depicted in FIGS.5 and 6 is a normally open valve.

The interior of the main spool 112′ of the proportional pressure controlvalve 310 differs from that of the proportional pressure control valve20. Formed through the entire length of the interior of the main spool112′ is a right circular cylindrically-shaped seat spool passage 322.When assembled into the proportional pressure control valve 310, theseat spool passage 322 of the main spool 112′ receives a rod-shaped seatspool 324 having a length that is greater than that of the main spool112′. The end of the seat spool 324 extending outward beyond thefeedback pressure surface 114′ of the main spool 112′ contacts the innersurface of the plug 92 and is surrounded by the coil spring 108′. Thus,in the proportional pressure control valve 310 the coil spring 108′presses against the feedback pressure surface 114′ of the main spool112′ and not against the seat spool 324.

The outer surface of the seat spool 324 enclosed within the main spool112′ near its feedback pressure surface 114′ is encircled by a trough326. The trough 326 establishes a hollow, annularly-shaped pilot valvesupply coupling chamber 328 encircling the seat spool 324 between theouter surface of the seat spool 324 and the surface of the seat spoolpassage 322. The pilot valve supply coupling chamber 328 forms part ofthe pilot valve supply passage 136′ to couple the portion of the pilotvalve supply passage 136′ passing through the main spool 112′ to theportion of the pilot valve supply passage 136′ passing through theinterior of the seat spool 324. Thus, as in the proportional pressurecontrol valve 20, the pilot valve supply passage 136′ of theproportional pressure control valve 310 is always open to a flow ofhydraulic fluid from the pump through the cage pump ports 56′ in thecage wall 44′.

Formed on the edge of the pilot valve supply passage 136′ passingthrough the seat spool 324 that extends outward through the controlpressure surface 138′ of the main spool 112′ is a beveled valve seat332. In the assembled proportional pressure control valve 310, a valveball 336 is juxtaposed with the valve seat 332 of the seat spool 324.The digital control signal proportional pressure control valve 310depicted in FIGS. 5 and 6 omits the screen 142 and the control flowrestriction orifice 144 included in the proportional pressure controlvalve 20 depicted in FIGS. 1 and 2.

The tube assembly 178′ of the proportional pressure control valve 310differs from the tube assembly 178 of the proportional pressure controlvalve 20 by substituting a solid tube plug 342 for the annularly-shapedthreaded tube plug 204.

The proportional pressure control valve 310 omits the coil spring 236″included in the proportional pressure control valve 20. Accordingly, theplunger 232′ of the digital normally open proportional pressure controlvalve 310 lacks the spring cavity 234 that is included in the plunger232 of the analog normally closed proportional pressure control valve20.

In the assembled proportional pressure control valve 310, a long pin 346and a short pin 348 extend outward coaxially from the plunger 232′through the interior of the pole piece 212′ toward the seat spool 324.The long pin 346 is preferably made from a non-magnetic material such asstainless steel or the like. To resist wear at the point of contactbetween the short pin 348 and the valve ball 336, the short pin 348 ispreferably made from a material such as hardened steel or a materialhaving similar wear resistant properties. The end of the short pin 348furthest from the plunger 232′ and nearest to the seat spool 324 isformed with a smaller diameter which allows it to enter freely into thecontrol pressure chamber outlet passage 162′ of the stop 152′. As may beappreciated by those skilled in the art, this same two-piece pinconfiguration may be utilized in the system illustrated on FIG. 2 andpreviously described above.

While in the proportional pressure control valve 20 the diameter of thecontrol pressure chamber outlet passage 162 in the stop 152 has auniform diameter throughout its entire length, the diameter of thecontrol pressure chamber outlet passage 162′ of the stop 152′ in theproportional pressure control valve 310 has an enlarged diameterimmediately adjacent to the valve seat 332 of the seat spool 324. Theenlarged diameter of the control pressure chamber outlet passage 162′immediately adjacent to the valve seat 332 provides a valve ballretaining chamber 354 analogous to the valve ball retaining chamber 226in the pole piece 212 of the proportional pressure control valve 20. AU-shaped slot 356 extends across the face of the stop 152′ immediatelyadjacent to the main spool 112′ and the seat spool 324. The slot 356forms a portion of the control pressure chamber 158′ that permitshydraulic fluid to flow into and out of the that portion of the controlpressure chamber 158′ adjacent to the control pressure surface 138′ ofthe main spool 112′. The diameter of the control pressure chamber outletpassage 162′ on the opposite side of the stop 152′ from the valve ballretaining chamber 354 that is adjacent to the pole piece 212′ is alsoenlarged to permit hydraulic fluid to flow freely about the short pin348 on its way to the body tank port 32′ and cage tank ports 52′, andthence to the tank.

Because the proportional pressure control valve 310 omits the coilspring 236″ included in the proportional pressure control valve 20,unless an electrical current flows through the solenoid coil 252′ thereis no force urging the plunger 232′ away from the solid tube plug 342toward the valve ball 336. Therefore, when no electrical current flowsthrough the solenoid coil 252′, the force of the hydraulic fluidimpinging on the valve ball 336 urges it away from the valve seat 332 ofthe seat spool 324 toward the interior of the stop 152′ and thenarrowest portion of the control pressure chamber outlet passage 162′.In this location, the valve ball 336 seals the control pressure chamberoutlet passage 162′ and hydraulic fluid at the full pressure supplied bythe pump fills the control pressure chamber 158′. The presence ofhydraulic fluid within the control pressure chamber 158′ at the fullpressure supplied by the pump causes the main spool 112′ to movelongitudinally within the cage 42 thereby coupling the cage pump ports56′ to the cage clutch ports 54′ to supply hydraulic fluid at the fullpressure supplied by the pump to the body clutch port 34′.

The magnetic field resulting from the application of a PWM electricalsignal to the solenoid coil 252′ pushes the plunger 232′ away from thesolid tube plug 342 toward the valve ball 336. The combined long pin 346and short pin 348 transmit this movement of the plunger 232′ to thevalve ball 336 pushing it toward the valve seat 332 of the seat spool324. Movement of the valve ball 336 toward the valve seat 332simultaneously allows hydraulic fluid to flow from the control pressurechamber 158′ into the control pressure chamber outlet passage 162′ andrestricts the flow of hydraulic fluid through the pilot valve supplypassage 136′ in the seat spool 324 into the control pressure chamber158′. Thus, a PWM electrical signal applied to the solenoid coil 252′reduces the pressure of the hydraulic fluid in the control pressurechamber 158′ thereby causing longitudinal movement of the main spool112′ within the cage 42′ that reduces the pressure of hydraulic fluidwithin the body clutch port 34′. Operated in this manner, the solenoidcoil 252′, the plunger 232′, the pins 346 and 348, the valve ball 336,the stop 152′, and the seat spool 324 provides an electromagneticallyoperated pilot valve for supplying a regulated pressure of fluid to thecontrol pressure chamber 158′ responsive to an electrical controlsignal.

FIG. 8 depicts a cross-sectional plan view of a proportional pressurecontrol valve referred to by the general reference character 410. FIG.7, made up of FIGS. 7A and 7B, is an exploded, cross-sectional plan viewdepicting the various parts included in the proportional pressurecontrol valve 410. Those elements depicted in FIGS. 7 and 8 that arecommon to the proportional pressure control valve 20 depicted in FIGS. 1and 2 or to the proportional pressure control valve 310 depicted inFIGS. 5 and 6 carry the same reference numeral distinguished by a doubleprime (“″”) designation. The same reference characters are used toidentify the same part of the proportional pressure control valve 410both in FIG. 7 and in FIG. 8. The proportional pressure control valve410 depicted in FIGS. 7 and 8 is a normally closed valve that is adaptedfor control by a digital pulse width modulated (“PWM”) electricalcontrol signal.

The tube 202″ of the proportional pressure control valve 410 is shorterthan the tube 202 of the tube assemblies 178 and 178′ of theproportional pressure control valves 20 and 310. Because of the shortertube 202″, the proportional pressure control valve 410 omits the spacer254. The solid tube plug 342″ of the proportional pressure control valve410 extends further into the tube 202″ than the tube plug 342 of theproportional pressure control valve 310 and functions as a pole piecefor the proportional pressure control valve 410. Formed into the end ofthe solid tube plug 342″ nearest to the adaptor 176″ is a plug springcavity 412. In the assembled proportional pressure control valve 410,the plug spring cavity 412 receives one end of the coil spring 236″. Theother end of the spring 236″ is received into the spring cavity 234″formed into the plunger 232″ of the proportional pressure control valve410 immediately adjacent to the solid tube plug 342″.

Projecting outward from the end of the plunger 232″ furthest from thespring cavity 234″ is a protrusion 422. A pin cavity 424, formed intothe protrusion 422, receives a pin 426. The outer surface of the plunger232″ parallel to the center line 24″ is not formed in the shape of afull right circular cylinder. Rather, the shape of the outer surface ofthe plunger 232″ parallel to the center line 24″ is similar to that ofthe plunger 232 as depicted in FIG. 3.

There are only two substantial differences between stop 152″ of thenormally closed proportional pressure control valve 410 and the stop152′ of the normally open proportional pressure control valve 310.Because the proportional pressure control valve 410 omits the pole piece212′ included in the proportional pressure control valve 310, the widthof the stop 152″ between the cage 42″ and the adapter 176″ is greaterthan that of the stop 152′. Thus, in the assembled proportional pressurecontrol valve 410, the adaptor 176″ contacts the stop 152″ and directlyforces it into the cage 42″ and holds it there. Also because theproportional pressure control valve 410 lacks the pole piece 212′, aU-shaped slot 432 is formed across the face of the stop 152″ immediatelyadjacent to the plunger 232″. The slot 432 forms a portion of thepassage by which hydraulic fluid, that flows out of the control pressurechamber 158″ through the control pressure chamber outlet passage 162″,returns to the body tank port 32″ and cage tank ports 52″, and thence tothe tank.

The coil spring 236 included in the proportional pressure control valve410 applies sufficient force to the valve ball 336″ through the plunger232″ and the pin 426 that, in the absence of an electric current flowingthrough the solenoid coil 252″, the valve ball 336″ seals the pilotvalve supply passage 136″ thereby preventing hydraulic fluid fromentering into and pressurizing the control pressure chamber 158″. Asexplained previously, the absence of any pressure on the hydraulic fluidin the control pressure chamber 158″ causes the proportional pressurecontrol valve 410 to block all fluid flow from the pump inlet chamber84″ to the body clutch port 34″ and relieves all pressure from thehydraulic fluid in the body clutch port 34″.

Application of a PWM signal to the solenoid coil 252″ of theproportional pressure control valve 410 overcomes the force applied tothe plunger 232″ of the spring 236″ and pulls the plunger 232″ away fromthe valve ball 336″ toward the solid tube plug 342″. Pulling the plunger232″ toward the solid tube plug 342″ releases the force urging the valveball 336″ into the valve seat 332″ of the seat spool 324″. The force ofthe hydraulic fluid impinging on the valve ball 336″ urges it away fromthe valve seat 332″ of the seat spool 324″ toward the interior of thestop 152″. Thus spaced apart from the valve seat 332″, the valve ball336″ allows hydraulic fluid to flow into and raise the pressure ofhydraulic fluid within the control pressure chamber 158″. Thepressurized hydraulic fluid within the control pressure chamber 158″causes the main spool 112″ to move laterally along the length of thecage 42″ and to couple the cage pump ports 56″ to the cage clutch ports54″ thereby supplying hydraulic fluid to the body clutch port 34″.Operated in this manner, the solenoid coil 252″, the plunger 232″, thepin 426, the valve ball 336″, the stop 152″, and the seat spool 324″provide an electromagnetically operated pilot valve for supplying aregulated pressure of fluid to the control pressure chamber 158″responsive to an electrical control signal.

A normally open proportional pressure control valve adapted for controlby an analog electrical control signal may be constructed bysubstituting certain elements from the normally closed proportionalpressure control valve 410 for elements of the normally closedproportional pressure control valve 20. Such a normally openproportional pressure control valve may be assembled by incorporatingthe tube assembly 178″, the spring 236″, and a plunger 232″ that lacksthe protrusion 422 of the proportional pressure control valve 410 forthe corresponding elements of the proportional pressure control valve20. The stop 152 of such an analog normally open valve must also bemodified from that included in the proportional pressure control valve20 by making it thicker so the adaptor 176 of the tube assembly 178 mayforce the stop 152 into the cage 42, and by providing structures thatwill support the valve ball 228 at the valve seat 164 analogous to thevalve ball retaining chamber 226 in the pole piece 212. The stop 152must also be modified to provide a passage by which hydraulic fluid,that flows out of the control pressure chamber 158 through the controlpressure chamber outlet passage 162, may return to the body tank port 32and cage tank ports 52.

In such a modified valve, of no current flows through the solenoid coil252, the force of the spring 236″ urges the valve ball 228 into sealingrelationship with the valve seat 164 thereby pressurizing the hydraulicfluid within the control pressure chamber 158. Supplying an analogelectrical control current to the solenoid coil 252 of such a modifiedvalve applies a magnetic field to the plunger 232″ that overcomes theforce of the spring 236 and pulls the plunger 232″ away from the valveball 228 thereby relieving the pressure of hydraulic field within thecontrol pressure chamber 158. Operated in this manner, the solenoid coil252″, the plunger 232″, the pin 426, the valve ball 228, the modifiedstop 152, and the control flow restriction orifice 144 provide anelectromagnetically operated pilot valve responsive to an analog currentfor supplying a regulated pressure of fluid to the control pressurechamber 158 responsive to an electrical control signal.

Referring now to FIG. 9, depicted there is a cross-sectional plan viewof a main spool 502 in accordance with the present invention that alsoincludes a pressure spike suppression check valve 504. Those elementsdepicted in FIG. 9 that are common to the main spool 112 of theproportional pressure control valve 20 depicted in FIGS. 1 and 2 carrythe same reference numeral distinguished by a triple prime (“″′”)designation.

The main spool 502 includes a narrow U-shaped trough 512 formed into theouter surface of the main spool 502 between the control pressure surface138″′ of the main spool 502 and the trough 122″′ that establishes thehollow, annularly-shaped valving chamber 124″′. The trough 512establishes a hollow, annularly-shaped pressure spike pilot chamber 514encircling the main spool 502 between its outer surface and the innersurface of the cage 42″′ (not illustrated in FIG. 9). The pressure spikepilot chamber 514 is always open to the cage tank ports 52″′ (notillustrated in FIG. 9). A pressure spike pilot valve cavity 518extending between the trough 122″′ and the control pressure surface138″′ opens into the pressure spike pilot chamber 514. The pressurespike pilot valve cavity 518 is open to the valving chamber 124″′through the surface of the trough 122″′. Threads formed at the end ofthe pressure spike pilot valve cavity 518 adjacent to the controlpressure surface 138″′ receive a threaded plug 522. The pressure spikesuppression check valve 504 fits snugly within the pressure spike pilotvalve cavity 518 to normally block any flow among the valving chamber124″′, the control pressure chamber 158″′ and the pressure spike pilotchamber 514 due to the pressure difference between the control pressurechamber 158 and valving chamber 124 and a spring 524 located betweenpressure spike suppression check valve 504 and the pressure spike pilotorifice 522. Spring 524 provides a biasing force to prevent unwantedoscillation of pressure spike suppression check valve 504.

If a clutch, or any other hydraulically operated device, reaches themechanical limit of its travel and hydraulic fluid flow through the cageclutch ports 54″ stops abruptly, the fluid pressure on the side of thepressure spike suppression check valve 504 open to the valving chamber124″′ rises abruptly. The pressure spike suppression check valve 504 isconstructed such that when the pressure of the hydraulic fluid on theside open to the valving chamber 124′ exceeds the pressure of thehydraulic fluid applied to the other side of the valve 504, the valve504 opens to permit fluid to flow between the valving chamber 124″′ andthe pressure spike pilot chamber 514. Since the pressure spike pilotchamber 514 is always open to the cage tank ports 52″′, fluid flows fromthe valving chamber 124″′ the cage tank ports 52 to relieve theabnormally high pressure within the cage clutch ports 54″′. When thepressure applied to the pressure spike suppression check valve 504 fromthe trough 122″′ once again equals or becomes less than the pressureapplied to the valve 504 from the control pressure surface 138″′, thepressure spike suppression check valve 504 once again closes to preventfluid from flowing between the valving chamber 124″′ and the pressurespike pilot chamber 514.

Industrial Applicability

While the disclosed embodiment describes certain preferred locations forvarious passages in the valve such as the pilot valve supply passage 136supplying hydraulic fluid from the cage pump ports 56 to the pilotvalve, and the feedback pressure passage 126 from the valving chamber124 to the feedback pressure chamber 118, those passages need notnecessarily be located exactly as described above. For example, thepilot valve supply passage 136 could be formed through the body 22 andthe adaptor 176 rather than through the main spool 112 in theproportional pressure control valve 20, or through the combined mainspool 112′ and the seat spool 324 in the proportional pressure controlvalve 310. Analogously, the feedback pressure passage 126 need not beformed through the main spool 112. Rather, the feedback pressure passage126 could be formed through the cage wall 44. Similarly, the pressurespike pilot valve cavity 518 could be formed through the cage wall 44″′and the pressure spike suppression check valve 504 be located in thecage 42″′ rather than in the main spool 502.

Comparatively large passages in the pilot valve of the proportionalpressure control valves 310 and 410 adapted for use with a PWM controlsignal permit omission of the screen 142 included in valves adapted forcontrol by an analog signal. If particles in the hydraulic fluid causeblockage of the passages in the valve 310 and 410, then a screen,similar to the screen 142 included in the proportional pressure controlvalve 20, may be suitably incorporated into either the main spool or theseat spool of the valves 310 or 410.

While the solenoid coil 252 of the proportional pressure control valvesadapted for control by an analog signal, a pulse width modulated (“PWM”)signal and the like, it may be desirable to use this valve as a solenoidon-off valve provided a small amount of bleeding flow is acceptable.Such an on-off valve assures the benefits of using a small inexpensivecoil to control comparatively large flow.

In distinction to the valves 20 and 310, the valve 410, when used in theproportional control mode, requires a pulse width modulated (“PWM”)driver with a “peak-and-hold” means to develop sufficient magneticforces to overcome the force provided by the compressed coil springwhich otherwise cannot be overcome at lesser values of current. It hasbeen determined that a usable pulse width modulation frequency rangewill be approximately from about 50 Hz to about 500 Hz.

While the body 22 has been described in connection with the preferredembodiment of the invention, the body 22 is not essential to thefunctioning of the valve. Rather, as described above, the body 22 merelyprovides a mechanical housing for the cage 42 and for joining the cage42 respectively with the pump, the tank and the clutch. Thus, a valve inaccordance with the present invention need not include the body 22.Rather, other structures, such as the case that mechanically enclosesthe transmission for an automotive vehicle, could itself directlyincorporate the structure and provide the function of the body 22 asdescribed above.

While the present invention has been described for use in hydraulictransmissions, its usefulness in other hydraulic systems will beunderstood by those skilled in the art of hydraulic systems. Such usesmay include but are not limited to hydraulic braking systems, hydrauliclifting systems and such similar hydraulic systems using proportionalcontrol valves.

Although the present invention has been described in terms of thepresently preferred embodiment, it is to be understood that suchdisclosure is purely illustrative and is not to be interpreted aslimiting. Consequently, without departing from the spirit and scope ofthe invention, various alterations, modifications, and/or alternativeapplications of the invention will, no doubt, be suggested to thoseskilled in the art after having read the preceding disclosure.Accordingly, it is intended that the following claims be interpreted asencompassing all alterations, modifications, or alternative applicationsas fall within the true spirit and scope of the invention.

What is claimed is:
 1. A proportional pressure control cartridge valvecomprising: a hollow cage having an axial direction and a radialdirection that includes a wall pierced in a direction substantiallyparallel to the axial direction of said cage by a pump port that isadapted for receiving hydraulic fluid from a pump at a pressureestablished by the pump, the wall also being pierced by clutch port in adirection substantially parallel to the radial direction of said cagethat is adapted for supplying pressurized hydraulic fluid to a hydraulicactuator, and the wall also being pierced in a direction substantiallyparallel to the radial direction of said cage by a tank port that isadapted for supplying hydraulic fluid to a tank; a spool means adaptedto fit snugly within said cage in which location said spool means ismoveable relative to said cage in a direction substantially parallel tosaid axial direction of said cage for controlling a flow of hydraulicfluid passing between the clutch port in said cage and either the pumpport or the tank port in said cage, said spool means including a controlpressure surface to which pressure may be applied for urging said spoolmeans to move within said cage to a position in which said spool meansallows a flow of hydraulic fluid to pass between the pump port and theclutch port, said spool means also including a feedback pressure surfaceto which pressure may be applied for urging said spool means to movewithin said cage to a position in which said spool means allows a flowof hydraulic fluid to pass between the clutch port and the tank port,said spool means further having a pilot valve supply passage formedtherein allowing the flow of hydraulic fluid in a directionsubstantially parallel to the axial direction of said cage that receivesa flow of hydraulic fluid from the pump port of said cage; a controlpressure chamber located within said cage for receiving fluid underpressure and applying the pressure of the fluid to the control pressuresurface of said spool means; an electromagnetically operated pilot valvemeans that receives a flow of hydraulic fluid passing through the pilotvalve supply passage of said spool means for supplying a regulatedpressure of fluid to said control pressure chamber responsive to anelectrical control signal; a feedback pressure chamber located withinsaid cage for receiving fluid at a pressure and coupling the pressure ofthe fluid to the feedback pressure surface of said spool means; and aclutch port pressure feedback passage for coupling the pressure ofhydraulic fluid within the clutch port in said cage to said feedbackpressure chamber, said clutch port pressure feedback passage including afeedback restriction orifice allowing the flow of hydraulic fluid in adirection substantially parallel to the axial direction of said cage forrestraining the rate at which fluid may flow between the clutch port insaid cage and said feedback pressure chamber.
 2. The proportionalpressure control cartridge valve of claim 1 wherein said pilot valvesupply passage supplies a control pressure flow of fluid from the pumpport to said control pressure chamber; said control pressure chamberhaving a control pressure chamber outlet through which fluid flows fromsaid control pressure chamber; and said electromagnetically operatedpilot valve means restraining the rate at which fluid flows from saidpilot valve supply passage into said control pressure chamber, andthereby regulating the pressure of the fluid within said controlpressure chamber.
 3. The proportional pressure control cartridge valveof claim 2 further comprising a control pressure flow return passage fordirecting the fluid that flows out of said control pressure chamberthrough the control pressure chamber outlet to the tank port of thevalve.
 4. The proportional pressure control cartridge valve of claim 1wherein said pilot valve supply passage supplies a control pressure flowof fluid from the pump port to said control pressure chamber, andwherein said pilot valve supply passage includes a control flowrestriction orifice for restraining the flow rate of the controlpressure flow of fluid; said control pressure chamber having a controlpressure chamber outlet through which fluid flows from said controlpressure chamber; said electromagnetically operated pilot valve meansrestraining the rate at which fluid flows from said control pressurechamber through the control pressure chamber outlet, and therebyregulating the pressure of the fluid within said control pressurechamber.
 5. The proportional pressure control cartridge valve of claim 4further comprising a control pressure flow return passage for conductingthe fluid that flows out of said control pressure chamber through thecontrol pressure chamber outlet to the tank port of the valve.
 6. Theproportional pressure control cartridge valve of claim 5, wherein saidpilot valve supply passage includes a removable screen.
 7. Theproportional pressure control cartridge valve of claim 5, wherein saidpilot valve supply passage includes an interchangeable orifice.
 8. Theproportional pressure control cartridge valve of claim 7, wherein saidpilot valve supply passage includes a removable screen between saidinterchangeable office and said pilot valve supply passage.
 9. Theproportional pressure control cartridge valve of claim 4, wherein saidpilot valve supply passage includes an interchangeable orifice.
 10. Theproportional pressure control cartridge valve of claim 4, wherein saidpilot valve supply passage includes a removable screen.
 11. Aproportional pressure control cartridge valve according to claim 4,wherein said pilot valve supply passage of said spool means receivessaid flow of hydraulic fluid from said pump port of said cage through aplurality of openings which connect said pilot valve supply passage withsaid pump port.
 12. The proportional pressure control cartridge valve ofclaim 11, wherein said pilot valve supply passage includes a removablescreen.
 13. The proportional pressure control cartridge valve of claim11, wherein said pilot valve supply passage includes an interchangeableorifice.
 14. The proportional pressure control cartridge valve of claim13, wherein said pilot valve supply passage includes a removable screen.15. The proportional pressure control cartridge valve of claim 1 whereinsaid pilot valve supply passage supplies a control pressure flow offluid from the pump port to said control pressure chamber; said controlpressure chamber having a control pressure chamber outlet through whichfluid flows from said control pressure chamber; said electromagneticallyoperated pilot valve means both restraining the rate at which fluidflows from said pilot valve supply passage into said control pressurechamber and restraining the rate at which fluid flows from said controlpressure chamber through the control pressure chamber outlet, andthereby regulating the pressure of the fluid within said controlpressure chamber.
 16. The proportional pressure control cartridge valveof claim 15 further comprising a control pressure flow return passagefor directing the fluid that flows out of said control pressure chamberthrough the control pressure chamber outlet to the tank port of thevalve.
 17. In a proportional pressure control cartridge valve thatincludes: a hollow cage having an axial direction and a radial directionthat includes a wall pierced by a pump port that is adapted forreceiving hydraulic fluid from a pump at a pressure established by thepump, the wall also being pierced by a clutch port that is adapted forsupplying pressurized hydraulic fluid to a hydraulic actuator, and thewall also being pierced by a tank port that is adapted for supplyinghydraulic fluid to a tank; the improvement comprising: said pump portpiercing said wall of said cage in a direction substantially parallel tothe axial direction of said cage; said clutch port and said tank portpiercing said wall in a direction substantially parallel to said radialdirection of said cage; spool means adapted to fit snugly within thecage in which location the spool means is moveable relative to the cagein a direction substantially parallel to the axial direction of saidcage for controlling a flow of hydraulic fluid passing between theclutch port in the cage and either the pump port or the tank port in thecage, the spool means including a control pressure surface to whichpressure may be applied for urging the spool means to move within thecage to a position in which the spool means allows a flow of hydraulicfluid to pass between the pump port and the clutch port, the spool meansalso including a feedback pressure surface to which pressure may beapplied for urging the spool means to move within the cage to a positionin which the spool means allows a flow of hydraulic fluid to passbetween the clutch port and the tank port, said spool means furtherhaving a relief valve supply passage formed therein that receives a flowof hydraulic fluid from the pump port of said cage; a control pressurechamber located within the cage for removing fluid under pressure andapplying the pressure of the fluid to the control pressure surface ofthe spool means; an electromagnetically operated pilot valve thatreceives a flow of hydraulic fluid passing through the relief valvesupply passage of said spool means for supplying a regulated pressure offluid to the control pressure chamber responsive to an electricalcontrol signal; a feedback pressure chamber located within the cage forreceiving fluid at a pressure and coupling the pressure of the fluid tothe feedback pressure surface of the spool means; a clutch port pressurefeedback passage for coupling the pressure of hydraulic fluid within theclutch port in the cage to the feedback pressure chamber; and a feedbackrestriction orifice allowing the flow of hydraulic fluid in a directionsubstantially parallel to the axial direction of said cage located inthe clutch port pressure feedback passage for restraining the rate atwhich fluid may flow between the clutch port in the cage and thefeedback pressure chamber.
 18. The proportional pressure controlcartridge valve of claim 17 further comprising a pilot valve supplypassage allowing the flow of hydraulic fluid in a directionsubstantially parallel to the axial direction of said cage for supplyinga control pressure flow of hydraulic fluid from the pump port to saidcontrol pressure chamber; said control pressure chamber having a controlpressure chamber outlet through which fluid flows from said controlpressure chamber; said electromagnetically operated pilot valve meansboth restraining the rate at which fluid flows from said pilot valvesupply passage into said control pressure chamber and restraining therate at which fluid flows from said control pressure chamber through thecontrol pressure chamber outlet, and thereby regulating the pressure ofthe fluid within said control pressure chamber.
 19. The proportionalpressure control cartridge valve of claim 18 further comprising acontrol pressure flow return passage for conducting the fluid that flowsout of said control pressure chamber through the control pressurechamber outlet to the tank port of the valve.
 20. The proportionalpressure control cartridge valve of claim 17 further comprising a pilotvalve supply passage allowing the flow of hydraulic fluid in a directionsubstantially parallel to the axial direction of said cage for supplyinga control pressure flow of hydraulic fluid from the pump port to saidcontrol pressure chamber; said control pressure chamber having a controlpressure chamber outlet through which fluid flows form said controlpressure chamber; said electromagnetically operated pilot valve meansrestraining the rate at which fluid flows from said pilot valve supplypassage into said control pressure chamber, and thereby regulating thepressure of the fluid within said control pressure chamber.
 21. Theproportional pressure control cartridge valve of claim 17 furthercomprising a pilot valve supply passage allowing the flow of hydraulicfluid in a direction substantially parallel to the axial direction ofsaid cage for supplying a control pressure flow of hydraulic fluid fromthe pump port to said control pressure chamber, said pilot valve supplypassage including a control flow restriction orifice for restraining theflow rate of the control pressure flow of hydraulic fluid; said controlpressure chamber having a control pressure chamber outlet through whichfluid flows from said control pressure chamber; said electronicallyoperated pilot valve means restraining the rate at which fluid flowsfrom said control pressure chamber through the control pressure chamberoutlet, and thereby regulating the pressure of the fluid within saidcontrol pressure chamber.
 22. The proportional pressure controlcartridge valve of claim 21 further comprising a control pressure flowreturn passage for conducting the fluid that flows out of said controlpressure chamber through the control pressure chamber outlet to the tankport of the valve.
 23. The proportional pressure control cartridge valveof claim 21, wherein said pilot valve supply passage includes aremovable screen.
 24. A method of operating a proportional pressurecontrol cartridge valve comprising the steps of: supplying pressurizedhydraulic fluid to a pump port formed through a wall of a hollow cage,wherein said hollow cage has an axial direction and a radial directionand said pump port allows the flow of hydraulic fluid in a directionsubstantially parallel to the axial direction of said cage; supplying aflow of hydraulic fluid from the pump port to an electromagneticallyoperated pilot valve through a pilot valve supply passage allowing theflow of hydraulic fluid in a direction substantially parallel to theaxial direction of said cage formed in a spool movable in a directionsubstantially parallel to the axial direction of said cage; supplying aregulated control pressure of fluid to a control pressure chamber withinthe cage which control pressure is regulated by an electrical controlsignal applied to the electromagnetically operated pilot valveproportional pressure control valve, the control pressure chamberincluding a control pressure surface located on the spool, the spoolfitting snugly within the hollow cage and being moveable therein in adirection substantially parallel to the axial direction of said cage,said control pressure applied to the control pressure surface urging thespool to move relative to the cage to a position in which the spoolallows a flow of hydraulic fluid to pass between the pump port in thewall of the cage to a clutch port also formed through the wall of thecage in a direction substantially parallel to the radial direction ofsaid cage while simultaneously obstructing any flow of hydraulic fluidbetween the clutch port and a tank port also formed through the wall ofthe cage in a direction substantially parallel to the radial directionof said cage; supplying a feedback pressure of fluid from the clutchport to a feedback pressure chamber within the cage, the feedbackpressure chamber including a feedback pressure surface on the spool,said feedback pressure applied to the feedback pressure surface urgingthe spool to move relative to the cage to a position in which the spoolobstructs any flow of hydraulic fluid between the pump port and theclutch port while simultaneously allowing a flow of hydraulic fluid topass between the clutch port and the tank port; and restraining the rateat which fluid may flow between the clutch port in the cage and thefeedback pressure chamber.
 25. The method for operating a proportionalpressure control cartridge valve of claim 24 wherein said regulatedcontrol pressure of fluid that is supplied to the control pressurechamber is generated by supplying a control pressure flow of fluid fromthe pump port to the control pressure chamber at a flow rate that isregulated in response to the electrical control signal applied to theproportional pressure control cartridge valve, and by allowing the fluidto flow out of the control pressure chamber at a rate that is alsoregulated in response to the electrical control signal.
 26. The methodfor operating a proportional pressure control cartridge valve of claim24, wherein said regulated control pressure of fluid that is supplied tothe control pressure chamber is generated by supplying a controlpressure flow of fluid from the pump port to the control pressurechamber at a flow rate that is regulated in response to the electricalcontrol signal applied to the proportional pressure control cartridgevalve, and by allowing the fluid to flow out of the control pressurechamber at a restrained flow rate.
 27. The method for operating aproportional pressure control cartridge valve of claim 24 wherein saidregulated control pressure of fluid that is supplied to the controlpressure chamber is generated by supplying a control pressure flow offluid from the pump port to the control pressure chamber at a restrainedflow rate, and by allowing the fluid to flow out of the control pressurechamber at a rate that is regulated in response to the electricalcontrol signal applied to the proportional pressure control cartridgevalve.
 28. A proportional pressure control cartridge valve for anautomatic transmission, said valve comprising: a hollow cage having anaxial direction and radial direction that includes a wall, said wallbeing pierced by: a pump port in a direction substantially parallel tothe axial direction of said cage, that is adapted for receivinghydraulic fluid from a pump at a pressure established by the pump, aclutch port in a direction substantially parallel to the radialdirection of said cage, that is adapted for supplying pressurizedhydraulic fluid to a hydraulic actuator, and a tank port in a directionsubstantially parallel to the radial direction of said cage, that isadapted for supplying hydraulic fluid to a tank; spool means forcontrolling a flow of hydraulic fluid passing between said clutch portand either said pump port or said tank port, said spool means adapted tofit snugly within said moveable in a direction substantially parallel tothe axial direction of said cage relative to said cage, said spool meanscomprising: a control pressure surface to which pressure may be appliedurging said spool means to move within said cage to a position in whichsaid spool means allows a flow of hydraulic fluid to pass between saidpump and said clutch port, a feedback pressure surface to which pressuremay be applied for urging said spool means to move within said cage to aposition in which said spool means allows a flow of hydraulic fluid topass between said clutch port and said tank port, and a relief valvesupply passage that receives a flow of hydraulic fluid from the pumpport and allows the flow of hydraulic fluid in a direction substantiallyparallel to the axial direction of said cage; a control pressure chamberlocated within said cage for receiving fluid under pressure and applyingthe pressure of the fluid to said control pressure surface; anelectromagnetically operated pilot valve means that receives a flow ofhydraulic fluid passing through said relief valve supply passage andallows the flow of hydraulic fluid in a direction substantially parallelto the axial direction of said cage for supplying a regulated pressureof fluid to said control pressure chamber responsive to an electricalcontrol signal; a feedback pressure chamber located within said cage forreceiving fluid at a pressure and coupling the pressure of the fluid tosaid feedback pressure surface; and a clutch port pressure feedbackpassage for coupling the pressure of hydraulic fluid within said clutchport to said feedback pressure chamber, said clutch port pressurefeedback passage including a feedback restriction orifice that allowsthe flow of hydraulic fluid in a direction substantially parallel to theaxial direction of said cage for restraining the rate at which fluid mayflow between said clutch port and said feedback pressure chamber.
 29. Anautomatic transmission comprising a proportional pressure controlcartridge valve for an automatic transmission, said valve comprising: ahollow cage that includes a wall, said wall being pierced by: a pumpport in a direction substantially parallel to the axial direction ofsaid cage that is adapted for receiving hydraulic fluid from a pump at apressure established by the pump, a clutch port in a directionsubstantially parallel to the radial direction of said cage, that isadapted for supplying pressurized hydraulic fluid to a hydraulicactuator, and a tank port in a direction substantially parallel to theradial direction of said cage, that is adapted for supplying hydraulicfluid to a tank; spool means for controlling a flow of hydraulic fluidpassing between said clutch port and either said pump port or said tankport, said spool means adapted to fit snugly within and moveable in adirection substantially parallel to the axial direction of said cagerelative to said cage, said spool means comprising: a control pressuresurface to which pressure may be applied for urging said spool means tomove within said cage to a position in which said spool means allows aflow of hydraulic fluid to pass between said pump port and said clutchport, a feedback pressure surface to which pressure may be applied forurging said spool means to move within said cage to a position in whichsaid spool means allows a flow of hydraulic fluid to pass between saidclutch port and said tank port, and a relief valve supply passage thatreceives a flow of hydraulic fluid from the pump port and allows theflow of hydraulic fluid in a direction substantially parallel to theaxial direction of said cage; a control pressure chamber located withinsaid cage for receiving fluid under pressure and applying the pressureof the fluid to said control pressure surface; an electromagneticallyoperated pilot valve means that receives a flow of hydraulic fluidpassing through said relief valve supply passage and allows the flow ofhydraulic fluid in a direction substantially parallel to the axialdirection of said cage for supplying a regulated pressure of fluid tosaid control pressure chamber responsive to an electrical controlsignal; a feedback chamber located within said cage for receiving fluidat a pressure and coupling the pressure of the fluid to said feedbackpressure surface; and a clutch port pressure feedback passage forcoupling the pressure of hydraulic fluid within said clutch port to saidfeedback pressure chamber, said clutch port pressure feedback passageincluding a feedback restriction orifice allowing the flow of hydraulicfluid in a direction substantially parallel to the axial direction ofsaid cage for restraining the rate at which fluid may flow between saidclutch port and said feedback pressure chamber.
 30. The proportionalpressure control cartridge valve of claim 29, wherein said pilot valvesupply passage includes a removable screen.